Distributed computing systems are made up of multiple interconnected processing nodes that cooperate to apply a common service to tasks. For distributed computing systems configured to implement a network service such as firewall or other virtual security service, load balancing, wide area network (WAN) optimization, Quality of Service (QoS), and network analysis and monitoring, for instance, each of the processing nodes may apply the network service to one or more packet flows that are associated in some manner to the processing node so that the processing node can consistently service the packet flow(s). Because a packet flow consists of multiple packets transmitted over time, the processing node that applies a network service to the packet flow should be associated to the packet flow for its duration, and each access node in the distributed computing system should consistently route the packets for the packet flow to the associated processing node.